I went with Roswell.
They are all nice Sims - but I could not chose Rosemary at all as I visualized her as being all about her education and Career and wanted nothing to hold her back like children and strong attachments. She has that serious look of one very focused and a life all about achievements. Rosemary wants to change the world with nothing standing in her way, especially commitments outside of her main focus. She look fiercely Independent.
I think of Generations Heirs as the family type - Roswell looked to me like a man whose family matters a lot and comes first - who is all about the family he wants and the family he was brought up in as well. The connection of both being very important to him. He would be an ideal heir.
Rosalee I could visualize a little of both - but I don't really see her as committed to a big family - maybe 1 child eventually - and having an fairly equal attachment to her future endeavors - as she may be to a family. I see her as more independent than Roswell and desires of maybe travels, artistry, living life with fewer anchors holding her back.
But this is how I view them just looking at these Sims and how I'd go about maybe playing these Sims stories if they were in my game. They may be very different - as this is just how I view them.